TW201418009A - Composite substrate - Google Patents

Abstract

A composite substrate (10) is obtained by bonding a supporting substrate (12) and a piezoelectric substrate (14) with each other, and the supporting substrate (12) and the piezoelectric substrate (14) are bonded with each other by an adhesive layer (16) in an embodiment of the present invention. Since the supporting substrate (12) of this composite substrate (10) is formed of a light-transmitting alumina ceramic, alignment during FCB can be easily done in comparison to the cases where a supporting substrate is formed of an opaque ceramic. In addition, it is preferable that the linear transmittance and the total forward light transmittance of the supporting substrate (12) in the visible light region (360-750 nm) are 10% or more and 70% or more, respectively.

Description

Composite substrate

The present invention relates to a composite substrate.

Conventionally, it has been known to form an elastic wave device in a composite substrate in which a support substrate and a piezoelectric substrate are bonded to each other. Here, the elastic wave device is used as a band pass filter, for example, in a communication device such as a mobile phone. Further, in the composite substrate, lithium niobate or lithium niobate is known as a piezoelectric substrate, and ruthenium or quartz or ceramic is used as a support substrate (see Patent Document 1). It is described that ceramics are widely used as packaging materials.

[advance technical documents] [Patent Document]

[Patent Document 1] Patent Publication No. 2006-319679

However, in the conventional composite substrate, since the support substrate is made of opaque ceramics, there is a problem that it is difficult to locate when flip chip bonding (FCB). Specifically, as shown in FIG. 6, at the time of flip chip bonding, the composite substrate 110 in which the support substrate 112 and the piezoelectric substrate 114 are bonded is placed on the piezoelectric substrate 114 with the piezoelectric substrate 114 on the lower side and the support substrate 112 on the upper side. Gold spherical bump 114a and printing The position of the electrode pad 102a on the substrate 102 is adjusted (positioned). The positioning is performed while confirming with the camera disposed on the side of the support substrate 112. At this time, although the piezoelectric substrate 114 is transparent, since the support substrate 112 is an opaque ceramic, it is not easy to be positioned by the support substrate 112.

The present invention has been made to solve such problems, and it is mainly aimed at providing a composite substrate which is easy to position at the time of FCB.

The composite substrate of the present invention is a composite substrate in which a support substrate and a piezoelectric substrate are bonded, and the material of the support substrate is a light-transmitting ceramic.

According to the composite substrate of the present invention, the positioning at the FCB becomes easier as compared with the case where the support substrate is made of an opaque ceramic. In other words, in general, the piezoelectric substrate is transparent. In the case of FCB, the piezoelectric substrate is lower and the supporting substrate is on. However, since the supporting substrate is made of translucent ceramic, the position of the piezoelectric substrate can be confirmed by the supporting substrate. The position of the spherical bump on the electric substrate, etc.). Therefore, it becomes easy to locate.

In the composite substrate of the present invention, the linear transmittance and the front total light transmittance in the visible light region (360 to 750 nm, the same applies hereinafter) of the support substrate are preferably 10% or more and 70% or more, respectively. Thus, the effects of the present invention described above can be obtained more reliably.

In the composite substrate of the present invention, the front total light transmittance of the support substrate is preferably 80% or more at a wavelength of 200 nm. When a photoresist film is formed on the surface of the piezoelectric substrate, the exposure of the photoresist film is performed using UV near the wavelength of 200 nm, and reflection at the interface between the piezoelectric substrate and the support substrate is suppressed. Can be patterned with high precision. Further, since the resolution of the exposure apparatus is defined by k × λ / NA (k: coefficient, λ: wavelength of the light source, NA: numerical aperture of the projection lens), and is exposed at a short wavelength, a fine pattern can be formed. Here, at least one of the front and back surfaces of the support substrate is preferably a rough surface (for example, an arithmetic mean roughness Ra of 5 to 20 nm). At this time, the value of the front total light transmittance at a wavelength of 200 nm becomes higher than when the front and back surfaces are mirror surfaces (for example, the arithmetic mean roughness Ra is 0.5 to 2 nm). In particular, it is preferable that both sides of the support substrate have a rough surface, and the value of the front total light transmittance at a wavelength of 200 nm is higher.

In the composite substrate of the present invention, the support substrate and the piezoelectric substrate are bonded via a bonding layer, and the refractive index of the bonding layer is preferably a value between a refractive index of the support substrate and a refractive index of the piezoelectric substrate. As described above, the light irradiated from above the piezoelectric substrate easily passes through the bonding layer and the supporting substrate.

In the composite substrate of the present invention, the support substrate may have a cast hole. When a support substrate is obtained by molding a raw material of a translucent ceramic and firing it, and a support substrate having a cast hole is produced, a mold for obtaining a molded body having a cast hole may be used. Therefore, the steps of masking and etching are not required. For example, when a tantalum substrate is used instead of a translucent ceramic substrate as a support substrate, in order to form a cast hole in the tantalum substrate, first, a single surface of the tantalum substrate (surface opposite to the surface on which the piezoelectric substrate is bonded) is covered with a photomask. , followed by exposure. It is necessary to develop a series of steps after developing the mask and then etching the unshielded portion.

In the composite substrate of the present invention, the thermal expansion coefficient of the support substrate is preferably 4 to 9 ppm/°C. Thus, the thermal expansion at a high temperature is small, and the temperature characteristic improvement effect is excellent.

In the composite substrate of the present invention, the average crystal of the above support substrate The particle diameter is preferably from 10 μm (micrometers) to 50 μm. Thus, since the average crystal grain size is small, unnecessary body waves can be reduced. Moreover, the UV transmittance and the strength also become high.

In the composite substrate of the present invention, the material of the support substrate is preferably a translucent alumina ceramic. The characteristics of the support substrate formed of the translucent alumina ceramic are as follows.

. Linear transmittance is more than 10% in the visible light region

. The front total light transmittance is 70% or more in the visible light region (80% or more at a wavelength of 200 nm), and the transmittance rapidly increases at a wavelength side shorter than the wavelength of 300 nm.

. Alumina purity above 99.9%

. Crystal grain size 10~50μm

. Thermal expansion rate 4~9ppm/°C

10‧‧‧Composite substrate

12‧‧‧Support substrate

14‧‧‧Piezoelectric substrate

16‧‧‧Connection layer

24‧‧‧Piezoelectric substrate

30‧‧‧1埠SAW resonator

32, 34‧‧‧IDT electrodes

36‧‧‧Reflective electrode

40‧‧‧Measurement device

41‧‧·score ball

42‧‧‧ tablet

44‧‧‧ points

46‧‧‧Light source

48‧‧‧Detector

102‧‧‧Printed substrate

102a‧‧‧Electrode pads

110‧‧‧Composite substrate

112‧‧‧Support substrate

114‧‧‧Piezoelectric substrate

114a‧‧‧Spherical bumps

S‧‧‧ samples

[Fig. 1] is a schematic perspective view showing a configuration of a composite substrate 10; [Fig. 2] is a perspective view showing a manufacturing step of the composite substrate 10; [Fig. 3] is a perspective view of a 1-inch SAW resonator 30 fabricated using the composite substrate 10. [Fig. 4] is a front total light transmittance spectrum of the supporting substrates A to C; [Fig. 5] is an explanatory diagram of the measuring device 40; and [Fig. 6] shows the loading of the composite substrate 110 to the printed substrate 102. State diagram of the previous time.

Next, the form for carrying out the invention will be described using the drawings. 1st The figure shows a schematic perspective view of the configuration of the composite substrate 10 of the first embodiment of the present invention.

As shown in FIG. 1, the composite substrate 10 is a bonding between the support substrate 12 and the piezoelectric substrate 14. In the present embodiment, the support substrate 12 and the piezoelectric substrate 14 are bonded by the bonding layer 16. This composite substrate 10 has a circular shape formed in one plane at one place. This planar portion, which is referred to as an orientation plane (OF), is used when performing the operations of the surface acoustic wave device in the manufacturing step of the surface acoustic wave device, for example, when performing wafer position and direction detection.

The support substrate 12 is a translucent alumina ceramic substrate having an alumina purity of 99% or more and a thermal expansion coefficient of 4 to 9 ppm/° C. The linear transmittance in the visible region of the support substrate 12 is 10% or more. Further, in the visible region of the support substrate 12, the front total light transmittance is 70% or more, and at a wavelength of 200 nm, it is 80% or more, preferably 85% or more, and more preferably 90% or more. The arithmetic surface roughness Ra of both surfaces of the support substrate 12 is 0.5 to 20 nm. Here, when both surfaces of the support substrate 12 are mirror surfaces (for example, Ra 0.5 to 2 nm), the single surface is a mirror surface, and the single surface is a rough surface (for example, Ra 5 to 20 nm) because the front total light transmittance is high. Ideally, both sides are rough because it is ideal for higher total light transmission in front. The average crystal grain size of the support substrate 12 is from 10 μm to 50 μm.

The piezoelectric substrate 14 is a substrate of a piezoelectric body that can transmit an elastic wave (for example, a surface acoustic wave). The material of the piezoelectric substrate 14 is, for example, lithium niobate, lithium niobate, lithium borate or crystal. These materials have a coefficient of thermal expansion of 13 to 16 ppm/°C. Such a piezoelectric substrate 14 is transparent.

The bonding layer 16 is a layer that bonds the support substrate 12 and the piezoelectric substrate 14. Although the material of the bonding layer 16 is not particularly limited, it is preferably an organic bonding agent having heat resistance, for example, an epoxy resin (EPOXY) series bonding agent, acrylic Series of bonding agents, etc. Further, the refractive index of the bonding layer 16 is a value between the refractive index of the support substrate 12 and the refractive index of the piezoelectric substrate 14. The bonding layer 16 has a thickness of 1 μm or less, preferably 0.2 to 0.6 μm.

An example of a method of manufacturing such a composite substrate 10 will be described below using FIG. Fig. 2 is a perspective view showing a manufacturing step of the composite substrate 10. First, a support substrate 12 having a predetermined diameter and thickness of OF is prepared. Moreover, the piezoelectric substrate 24 having the same diameter as the support substrate 12 (see FIG. 2(a)). The piezoelectric substrate 24 is thicker than the piezoelectric substrate 14. Then, at least one of the surface of the support substrate 12 and the back surface of the piezoelectric substrate 24 is uniformly applied with a bonding agent. After that, the two substrates 12 and 24 are joined together, and when the bonding agent is a thermosetting resin, it is heat-cured, and when the bonding agent is a photocurable resin, it is irradiated with light to form a bonding agent 16 (see FIG. 2(b)). Thereafter, the piezoelectric substrate 24 is polished to a predetermined thickness by a grinder, and the composite substrate 10 is obtained as the piezoelectric substrate 14 (see FIG. 2(c)).

The composite substrate 10 thus obtained is formed by using a general lithography technique, and the composite substrate 10 is formed as an aggregate of a plurality of surface acoustic wave devices, and then cut out by one surface acoustic wave device according to the timing. The state in which the composite substrate 10 is an aggregate of the 1 埠 SAW resonator 30 of the surface acoustic wave device is shown in FIG. The 1-inch SAW resonator 30 forms IDT electrodes 32, 34 and a reflective electrode 36 on the surface of the piezoelectric substrate 14 in accordance with a lithography technique. The IDT electrodes 32, 34 are formed, for example, as follows. First, a photoresist is applied on the upper surface of the piezoelectric substrate 14, and light is irradiated onto the photoresist through the photomask. Next, the imaging solution is immersed to remove unwanted photoresist. When the photoresist is a negative photoresist, the portion of the photoresist that is illuminated remains on the piezoelectric substrate 14. On the other hand, when the photoresist is a positive photoresist, a portion of the photoresist which is not illuminated remains on the piezoelectric substrate 14. Next, the electrode material (for example, aluminum) is vapor-deposited in total, and the comb-shaped IDT electrodes 32, 34 are obtained by removing the photoresist. The IDT electrode 32 is a + pole, and the IDT electrode 34 is a pole which is alternately arranged to form a pattern. Then, the interval (period interval) between adjacent + poles corresponds to the wavelength λ, and the value of the speed of sound v divided by the wavelength λ corresponds to the resonance frequency fr.

According to the composite substrate 10 of the present embodiment described above in detail, since the support substrate 12 is made of a translucent alumina ceramic, it is easier to position the FCB than when the support substrate is made of an opaque ceramic. In the FCB, the transparent piezoelectric substrate 14 is below and the support substrate 12 is on. However, since the support substrate 12 is made of translucent ceramic, the position of the piezoelectric substrate 14 can be confirmed by the support substrate 12 (on the piezoelectric substrate 14). Set the position of the gold spherical bumps, etc.). Therefore, it becomes easy to locate. Further, in the composite substrate 10, since the linear transmittance and the front total light transmittance in the visible light region of the support substrate 12 are respectively 10% or more and 70% or more, such an effect can be obtained more reliably.

Further, since the thermal expansion coefficient of the support substrate 12 is smaller than that of the piezoelectric substrate 14, the change in the size of the piezoelectric substrate 14 at the time of temperature change is suppressed by the support substrate 12. Therefore, the change in the frequency characteristics can be suppressed with respect to the temperature of the elastic wave device fabricated using the composite substrate 10. In particular, in the composite substrate 10, since the thermal expansion coefficient of the support substrate 12 is 4 to 9 ppm/° C., thermal expansion at a high temperature is small, and the effect of improving the temperature characteristics of the elastic wave device is excellent.

Further, the total light transmittance of the front surface of the composite substrate 10 was 80% at a wavelength of 200 nm. Therefore, after the photoresist film is formed on the surface of the piezoelectric substrate 24, the exposure of the photoresist film is performed using UV at a wavelength of about 200 nm, and reflection in the interface between the piezoelectric substrate 24 and the support substrate 12 is suppressed, and high precision can be achieved. pattern Chemical. Further, since the resolution of the exposure apparatus is defined by k × λ / NA (k: coefficient, λ: wavelength of the light source, NA: numerical aperture of the projection lens), and is exposed at a short wavelength, a fine pattern can be formed.

Further, since the refractive index of the bonding layer 16 is a value between the refractive index of the supporting substrate 12 and the refractive index of the piezoelectric substrate 14, light irradiated from above the piezoelectric substrate 14 easily passes through the bonding layer 16 and the supporting substrate. 12.

Further, since the average crystal grain size of the support substrate 12 is 10 μm (micrometer) to 50 μm, unnecessary body waves can be reduced. Moreover, the UV transmittance and the strength also become high.

Further, the present invention is not limited to the above embodiment, and it is needless to say that it can be implemented in various forms as long as it falls within the technical scope of the present invention.

For example, in the above-described embodiment, the case where the surface acoustic wave device which is one of the elastic wave devices is fabricated using the composite substrate 10 will be described, but other laminated substrates such as a lamb wave device and a thin film resonator may be fabricated using the composite substrate 10. (FBAR) elastic wave device.

In the above-described embodiment, the support substrate 12 and the piezoelectric substrate 14 are joined by the bonding layer 16 to form the composite substrate 10. However, the bonded support substrate 12 and the piezoelectric substrate 14 may be directly bonded to each other to form a composite substrate. When the two substrates 12 and 14 are bonded by direct bonding, for example, the following methods are exemplified. That is, first, the joint faces of the two substrates 12 and 14 are cleaned, and the impurities (oxides, adsorbates) adhering to the joint faces are removed. Next, by irradiating the two substrates 12 and 14 with an ion beam of an inert gas such as argon to the joint surface of the both substrates, the remaining impurities are removed and the joint surface is activated. Thereafter, the two substrates 12, 14 are joined at room temperature in a vacuum.

In the above embodiment, the support substrate 12 may have a cast hole. When the support substrate 12 is obtained by molding a raw material of a translucent alumina ceramic and firing it, and a support substrate 12 having a cast hole is produced, a mold such as a molded body having a cast hole may be used. Therefore, the steps of masking and etching are not required. For example, when a tantalum substrate is used instead of a translucent alumina ceramic substrate as the support substrate 12, in order to form a cast hole in the tantalum substrate, first, a single surface of the tantalum substrate is covered with a photomask (opposite side to the surface on which the piezoelectric substrate is bonded) Face), followed by exposure. It is necessary to develop a series of steps after developing the mask and then etching the unshielded portion.

In the above embodiment, the support substrate 12 is assumed to be a translucent alumina ceramic substrate, but the support substrate 12 may be a translucent ceramic substrate other than alumina. In this case as well, the effect of being easily positioned when the FCB is obtained is also obtained.

[Examples]

[Translucent alumina substrate (support substrate A~C)]

A translucent alumina substrate having a diameter of mm 100 mm (mm) was prepared by the following method. Initially, a slurry of the components of Table 1 was prepared. Further, the α-alumina powder is a powder having a specific surface area of 3.5 to 4.5 m ² /g and an average primary particle diameter of 0.35 to 0.45 μm.

This slurry was poured into a mold made of an aluminum alloy at room temperature, and then allowed to stand at room temperature for 1 hour. Next, it was left at 40 ° C for 30 minutes, and after solidification, it was released. Further, they were allowed to stand at room temperature and then at 90 ° C for 2 hours to obtain a plate-shaped powder molded body. The obtained powder molded body was calcined at 1100 ° C in the air (pre-baked), and then the calcined body was placed on a molybdenum plate, and a gap of 0.1 to 0.5 mm was left on the upper side, and hydrogen: nitrogen = 3:1. In the air (volume ratio), it is fired at 1700 to 1800 °C. Thereafter, the fired body is placed on a molybdenum plate, and a weight of molybdenum is loaded thereon, and tempering is performed at 1700 to 1800 ° C in air of hydrogen:nitrogen=3:1 (volume ratio). At the time of baking, by leaving a gap on the upper side, discharge additive (mainly magnesium oxide or the like) is performed, and the load (heating weight) is burned by tempering treatment and tempered at the same temperature to promote the refinement. Thus, a light-transmitting alumina substrate was obtained.

Three such translucent alumina substrates are prepared, and the first substrate is polished on both sides (hereinafter referred to as support substrate A), and the second substrate is polished on both sides (hereinafter referred to as support substrate B). The single-sided polished, single-sided polished support substrate (hereinafter referred to as support substrate C). The grinding system was performed using diamond abrasive grains, #1500 grinding stone. The polished surface was ground and polished using diamond abrasive grains having an average particle diameter of 0.5 μm, and the surface was polished using a colloidal sol (Colloidal Silica) polishing liquid and a rigid polyurethane pad. Regarding each of the support substrates, the arithmetic mean roughness (Ra) was measured with a tip-type surface roughness measuring instrument. Further, the front total light transmittance is measured by the measuring device 40 of Fig. 5 which will be described later. These knots The results are shown in Table 2. In Fig. 4, the front total light transmittance spectrum is displayed. Further, the average crystal grain size, the thermal expansion coefficient, and the linear transmittance in the visible light region of each of the support substrates were measured. These results are also shown in Table 2.

Further, the front total light transmittance is calculated based on the measured value obtained by the measuring device 40 of Fig. 5. In the measuring device of Fig. 5, the opening of the integrating sphere 41 is plugged with the sample S (thickness: 3 mm), and a thin plate having a hole 44 (diameter ψ 3 mm) is placed on the upper surface of the sample S. In this state, the sample is passed through the hole 44. S illuminates the light from the light source 46, and the light passing through the sample S is collected using the integrating sphere 41, and the intensity of the light is measured by the detector 48. The front full light transmittance is obtained according to the following formula.

Front total light transmittance = 100 × (measured light intensity) / (intensity of light source)

[First Embodiment (Composite Substrate)]

Above the support substrate A, an epoxy resin (EPOXY) series bonding agent having a refractive index of 1.9 is applied at a thickness of 1 μm or less using a spinner. When the refractive index of the bonding agent is between LiTaO ₃ (refractive index 2.1) and translucent alumina (refractive index of 1.7), light irradiated from above LiTaO ₃ is easily passed (light transmittance is improved). And support substrate A. Therefore, an epoxy resin (EPOXY) series bonding agent having a refractive index of 1.9 was used. A 42Y-X LiTaO ₃ piezoelectric substrate having a thickness of 230 μm (a 42° Y-sheet X-transferred LiTaO ₃ piezoelectric substrate having a cutting angle of a rotating Y-piece) prepared separately from the support substrate A was fired at a temperature of about 150 ° C. to make. The surface of the piezoelectric substrate was roughly ground by grinding, and the thickness of the piezoelectric substrate was thinned to 25 μm. Further, the same surface was surface-polished by using Colloidal Silica and a rigid polyurethane pad to precisely polish the surface. The piezoelectric substrate at this time had a thickness of 20 μm. Finally, a furnace at 250 ° C was placed, and the bonding agent was completely cured to form a composite substrate.

On the piezoelectric substrate of the composite substrate, a comb-shaped IDT electrode made of aluminum was formed by lithography to form a SAW resonator. The IDT electrode was formed by a peeling method using an exposure machine of ArF having a wavelength of 193 nm. The peeling method initially applies a negative photoresist on the surface of the piezoelectric substrate, and irradiates the light through the photomask to the negative photoresist. Next, the imaging solution is immersed to remove the unwanted negative photoresist. Therefore, the portion of the light in the negative photoresist remains on the piezoelectric substrate. Next, Al (aluminum) of the electrode material is completely vapor-deposited, and the negative photoresist is removed, whereby an IDT electrode of a desired pattern is obtained. The period interval of the IDT electrode is assumed to be 4.5 μm. The obtained SAW resonator was measured by a network analyzer, and as a result, a resonance frequency was obtained at around 920 MHz at room temperature. Further, the SAW resonator was placed in a constant temperature bath to change the temperature at -20 to 90 ° C, and the resonance frequency at that time was measured. Based on these measurement data, TCF (frequency temperature coefficient) was calculated and found to be -25 ppm/°C, and an improvement in temperature characteristics of about 15 ppm/° C. was obtained as compared with the SAW resonator of the LT single plate. Improve the graph by using short wavelengths The accuracy of the case can also reduce the instability of the resonator frequency caused by the instability of the electrode period interval.

[Comparative Example 1 (composite substrate)]

A support substrate was used, and a Si substrate was used instead of the translucent alumina substrate. A composite substrate was produced in accordance with the method of the first embodiment, and a SAW resonator was fabricated on the piezoelectric substrate. When the lithography process is exposed, UV light is reflected at the joint interface between the piezoelectric substrate and the support substrate, and the patterning accuracy of the IDT electrode is deteriorated compared to the first embodiment. Therefore, the resonator frequency becomes unstable compared to the first embodiment.

The present application is based on the priority of the United States Patent Application No. 61/658,988 filed on Jun. 13, 2012, the entire content of which is hereby incorporated by reference.

The present invention can be applied to a surface acoustic wave device or an elastic wave device such as a lamb wave device or a thin film resonator (FBAR).

10‧‧‧Composite substrate

12‧‧‧Support substrate

14‧‧‧Piezoelectric substrate

16‧‧‧Connection layer

OF‧‧‧ Orientation plane

Claims (7)

A composite substrate that bonds a support substrate and a piezoelectric substrate, wherein the material of the support substrate is a translucent ceramic. The composite substrate according to claim 1, wherein the visible light region (360 to 750 nm (nanometer)) of the support substrate preferably has a linear transmittance and a front total light transmittance of 10% and 70%, respectively. . The composite substrate according to claim 1 or 2, wherein the front substrate has a total light transmittance of 80% or more at a wavelength of 200 nm. The composite substrate according to claim 3, wherein the arithmetic mean roughness Ra of at least one of the front and back surfaces of the support substrate is 5 to 20 nm. The composite substrate according to any one of claims 1 to 4, wherein the support substrate and the piezoelectric substrate are bonded via a bonding layer, and a refractive index of the bonding layer is a refractive index of the support substrate and the pressure. The value between the refractive indices of the electrical substrate. The composite substrate according to any one of claims 1 to 5, wherein the support substrate has a cast hole. The composite substrate according to any one of claims 1 to 6, wherein the material of the support substrate is a translucent alumina ceramic.